Tubular elements made of quartz glass or of quartz-ceramic materials are used in many applications, particularly in laboratories, and as components in various types of chemical and other apparatus. To connect tubes and pipes of such material together by flange connection causes difficulties since the material is brittle and difficult to shape. It has been proposed to connect tubular elements of quartz-type material together by forming flanges on the pipes or tubes to be connected, interposing a compressible sealing ring between the elements, and clamping the flanges to each other by means of external clamping rings, which surround the pipes or tubes. The flange may be formed as an externally projecting ring, or as a conical enlargement in the region of the flange connection. Such flange connections are illustrated, for example, in the prospectus Q-C 1/112, 1974, issued by Heraeus Quarzschmelze GmbH. The tubular element, during manufacture, has the ring-shaped flange thickening or projection formed thereon, the thickening projections then retaining the metal clamping flange which is placed thereabout. The flange projection itself can be made as desired in conical form, as a ring-shaped projection having an essentially rectangular cross section, or in other forms.
It has been found in operation that connecting tubes or pipes of quartz-type material by means of a projecting flange causes difficulties if the pipe has an inner diameter exceeding about 18 inches (45 cm), and having a wall thickness in excess of about 5/8 inch (15 mm).